The Afterward: Edramore has an aneurysm that no magic healing is able to safely cure. As this could rupture to kill him at any time, he's keen to marry again so he's daughters will have a good stepmother if he's dead (their mother, his first wife, is already deceased). Kalanthe, his intended, finds it moving how he considers her such a responsible candidate for becoming his wife. He's understanding of her being a lesbian as well, agreeing they won't have sex either. Edramore dies suddenly in his sleep when Kalanthe's still considering his proposal, with his servants and daughters devastated by this.
In And Then There Were None, the culprit, Lawrence John Wargrave, was dying anyway. In fact, this trope is the motivation behind the plot: Wargrave was a Hanging JudgeKnight Templar who reunited ten Karma Houdinis in the same place and engineered their deaths to punish them for their deeds.
Taken literally in Animorphs when the last of the Arn, who are extremely adept in biology, is capable of pinpointing to the exact day how long he expects himself to live. As the Animorphs don't trust the Arn, Ax gives the subtle threat that "biology isn't the only factor".
Blue Castle by L.M. Montgomery Valancy Stirling is 29, unloved, and considered a burden by her wealthier relatives. Experiencing chest pains she sneaks off to see the "other doctor" in town that no one in the family will have anything to do with because he bluntly told one of her wealthier relatives that her illness was caused by self-involvement and to help others. He examines her but runs out mid-exam. The nurse tells Valancy that there has been a horrible accident and the doctor was rushing to attend to the injured. A few days later she receives a letter from him giving her less than a year to live. No longer having to worry about being supported by wealthier she rebels first in small ways like back talking, but eventually, she runs off to care for an old classmate that is dying of consumption, after having had a baby out of wedlock. From there marries the local rogue. When she finds out the letter was a mistake meant for an older woman named Miss Sterling, she fears her husband will think she tricked him on purpose.
Books of the Raksura: The titular Humanshifting race's scales turn white when they're close to dying from old age. In The Serpent Sea, Flower brushes off the signs and uses her final days to help secure a new, safe home for her colony.
Most of the cast gets this treatment in The Book Thief. Well, technically all of them are under this trope (see Real Life) since Death is the narrator, but we also know most of them die young.
Buffy the Vampire Slayer: In The Gatekeeper Trilogy, Jean -Marc, the current Gatekeeper, is dying of old age throughout the events of the trilogy and needs to get his son and heir Jacques back to the Gatehouse in time for Jacques to take over from Jean-Marc once the latter dies and prevent their mission from failing. Jean-Marc is wounded while fighting Il Maestro's cultists, which further shortens his lifespan.
In The Butterfly Garden, the girls have until their twenty-first birthday in the Garden. The Gardener only collects teenage girls and kills them before they lose their beauty, then immortalizes them in resin and places them on display in the Glassy Prison with the other girls.
The plot of Charlotte's Web involves a spring pig, Wilbur, learning he's going to be slaughtered for Christmas dinner and it's up to a spider, Charlotte, to praise him with her web so he can live his life. Wilbur is saved, but then this trope applies to Charlotte, who knows that she'll die soon after she lays her eggs.
In City of Ashes, when Clary destroys Valentine's ship with a single mark, an awed Valentine says "Mene mene tekel upharsin", in reference to the Biblical quote below. It's given an Ironic Echo later in City of Glass when Clary engineers the failure of all his plans as well as his own death. He's sealed her mouth, so she writes "MENE MENE TEKEL UPHARSIN" in the sand at his feet.
In "The Cold Equations" by Tom Godwin, an 18-year-old girl sneaks onto a space shuttle on a lark. But the ship doesn't have enough fuel to land with her on board. Either she goes out the airlock, voluntarily or otherwise, or the ship will crash. The universe doesn't care which. Published in 1954, the story subverted the usual notion in Golden Age science fiction that all problems could be solved through the power of Science.
Subverted in the Discworld series, where the anthropomorphic personification of Death has an hourglass for every living being on the Disc, counting down accurately to their death... except the wizard Rincewind, whose personal timeline is so messed up at this point that not even Death knows when he'll die.
Wizards and witches also have pre-emptive knowledge of when they're going to die, and thus tend to use this knowledge to put their affairs in order. Witches use it to make sure a replacement is found, bequeathing her personal items, making sure a grave is dug, and so on, while wizards tend to borrow large amounts of money from their friends and drink themselves into a stupor. Both sides like to throw a good last party with their friends/colleagues as well.
To be specific, they are evidently forewarned about their imminent natural deaths. Just because they haven't sensed this trope in action doesn't mean they can't get themselves killed by doing something reckless or stupid, or be killed by somebody else who couldn't care less if they're bumping up the schedule.
Albert (Death's manservant), when he realized he was going to die soon, performed the Rite of AshkEnte, which summons Death, in reverse, hoping to keep Death away, but instead transporting him to Death's domain (which may have been his actual intention). He's effectively immortal there, but if he ever returns to the world, the time he has left (about three months) will start passing again. After the events of Soul Music, his lifetimer is smashed and Death manages to save a few seconds of time in a beer bottle: if Albert ever returns to the Disc again, he'll die immediately. Though the normal rules of time are suspended during Hogswatch Night, so the Hogfather can make all his deliveries in one night, which allows Albert to tag along with Death when he's Subbing For The Hogfather.
The lifetimers are physical objects, and rather fragile at that. Several are destroyed and/or fall to the ground and smash during the course of Death's fight with Mort, which makes the nearest convenient death occur instantly (although one man who almost dies of falling is caught on a tree branch because one of the other characters catches his lifetimer).
Also, at least one being on the Disc can ignore lifetimers at will - Death himself. In addition to the old trick of simply not collecting the dead in question, at one point Death turns over Mort's lifetimer, giving him extra time.
But Death is specifically not supposed to do that, leading to a scene in Hogfather, when it's time for The Little Match Girl to die in a cold, dark alley, and Death is having to spend the night pretending to be the Hogfather. Instead of taking her soul, he extends her life, via Loophole Abuse: Death's not allowed to do that, but the Hogfather can. The Hogfather gives presents. There's no better present than a future.
Dracula: Lucy Westenra's mother has an undefined heart condition that her doctor says will kill her within months, or immediately if she receives a suitably large shock. This forces the rest of the characters to keep Lucy being attacked by Dracula from Mrs. Westenra out of concern it will trigger her condition.
In End of Watch, Bill Hodges learns that he has late-stage pancreatic cancer that has metastasized to his liver, and is given only a year or two at best. As the book progresses he is in increasing pain, to the point that it's a struggle for him to confront the villain in the climax. He does survive to the end of the main story but dies in the epilogue, only eight months later.
Occurs to the male protagonists of Hammerjack and its sequel Prodigal. Cray Alden's body is being gradually but irreversibly transformed due to being infected with Ascension-grade Flash, and Nathan Straka is forced to administer himself a massive drug overdose that prevents his brain implant from being hacked but which will be fatal within days.
Harry Potter: Albus Dumbledore was slowly dying of a horrible curse in Half-Blood Prince and arranged a quick and easy death with Severus Snape as part of an elaborate Thanatos Gambit (though this isn't revealed until Deathly Hallows). Harry himself found out that he was one of Voldemort's Horcruxes, and would also have to die if Voldemort was to be rendered mortal once more. Though fortunately the circumstances of his sacrifice (and the incredibly foolish decision on Voldemort's part to restore his body using Harry's blood back in Goblet of Fire) allowed Harry to survive it.
In the Hayven Celestia universe geroo serving on Generation Ships are euthanized at the age of sixty, criminals commonly have years deducted from their remaining lifespan. In the first chapter of Traitors, Thieves, and Liars Captain Ateri is two weeks from his "retirement" date and his chosen successor is very much not ready yet.
In The Alchemist by H. P. Lovecraft, each member of the Hereditary Curse dies at the age of 32. It is manually enforced by Charles Le Sorcier. The curse is broken when the last of the line decides to explore the castle and find the secret alchemist's laboratory.
In The Infernal Devices, Jem is addicted to a drug (yin fen) that is slowly killing him. However, to stop taking the drug will also kill him.
It takes Gilgamesh a long time to accept that he has to die, but once he does, life somehow gets better for him.
Conversed with Nicolae Carpathia and Buck Williams in the Dramatic Audio version of the Left Behind book Desecration.
Anyone who takes the Mark of the Beast and worships his image in the series is also in the same state.
In Robert Heinlein's short story Life Line, someone invents a machine that can tell you exactly what that number is. The life insurance companies are not amused.
The machine gets referenced in his later novel Methuselah's Children when Lazarus Long claims to have tried it out once, the device's owner refused to share the readout as he was sure it was malfunctioning.
Elizabeth aka Beth realizes her days are numbered in Little Women Part Second and spends her last year in a room that her family has turned into a little corner of paradise for her before the inevitable Tear Jerker death scene.
The Machineries of Empire: Kel generals can invoke the Vrae Tala clause to override the psychic conditioning that would force them to obey untenable or impossible orders, but slowly sicken and die 100 days later. Throughout the countdown, their troops place memorial candles by their seat at the high table in recognition.
The narrator of Jack Ritchie's "For All the Rude People" is diagnosed with a terminal illness which gives him two or three months to live, if he's lucky. He decides to spend his remaining time disposing of everyone who's ever been exceptionally rude to other people.
In The Nekropolis Archives novel Nekropolis, the preservation spells which sustain zombie protagonist Matthew Richter's body are beginning to fail, leaving him with only a few days left before he rots away.
Orlando Gardiner in Otherland is a teenage boy with progeria, a genetic disease that causes rapid aging and is invariably fatal. He lives his life mainly online, playing a virtual hero while his real body wastes away.
Sarah from Nemesis inherited her grandfather's powers that he got from a Super Serum but is also dying because of them. Two of her three brothers are already dead and she claimed that she's been ready to die since she was four years old.
Pact plays with this trope. Initially, the reader is led to believe that Rose, the Distaff Counterpart of the protagonist who is trapped in a mirror world, is going to die eventually because she's a fundamentally unstable copy of Blake, who will eventually degrade and vanish. However, it turns out that it's actually Blake whose days are numbered-he's fated to die, and when he does Rose will be able to take his place in the real world.
The Raven Tower: The Raven's Lease is the highest authority in the city, but is required to commit ritual suicide when the raven possessed by the eponymous Physical God dies. The narration dryly notes that ambitious people tend to set their sights on positions with slightly less power but a longer tenure.
Retired Witches Mysteries: People who become ghosts can spend up to one hundred years on Earth before they have no choice but to move on. The Grand Council of Witches discourages them from sticking around at all though, especially witches.
Whoever watches the cursed videotape in The Ring (the original book as well as the movies) will die in seven days unless they figure out how to break the curse. Likewise, Samara/Sadako probably figured that being stuck at the bottom of a well boded ill for her chances of survival.
Secret Vampire: Poppy finds out relatively early on that she has pancreatic cancer and it's inoperable. The doctors believe she will likely only have three months to live, tops, meaning she won't live past the summer she was so looking forward to.
Cinderpelt is told she's going to die by StarClan as a Secret Test of Character. She passes and is reincarnated as one of the newborn kits she died protecting.
A medicinecat told Shellheart that the painful lump in his stomach was impossible to survive from. Shellheart died two months after he was told this.
All men with the ability to channel are doomed to madness and death by the God of Evil's taint on the male half of the One Power, usually within a few years of beginning to channel, so Rand's army of male channelers hope for nothing more than to die winning the impending Final Battle. When Rand cleanses the taint, they're gobsmacked at the realization that they could live in the new world they're fighting for.
The Bloodknives are an elite group of assassins, each equipped with an Artifact of Death ring that drastically boosts their combat and stealth abilities but kills them within a month of its activation. Gawyn activates three such rings at once in an attempt to kill a devastatingly powerful enemy. He fails.
Terry Brooks played with this trope in The Wishsong of Shannara. Bremen informs Allanon that if he continues with the quest the heroes are on, he will not live to see its end. Bremen also informs him what it will be that kills him and why it must happen. Allanon isn't thrilled with this news and, briefly, does try to avoid a confrontation with his future killer. When he accepts his death is inevitable and absolutely necessary, he chooses to Face Death with Dignity thus ensuring that the Cycle of Magic can come to a close once the quest is completed.
